Method and apparatus for transporting ethernet services

ABSTRACT

Frames of customer traffic may be encapsulated by adding Mac-in-Mac (MiM) encapsulation fields for transportation of the frames over a portion of provider network. The MiM encapsulated traffic may be further encapsulated using VPLS by adding VPLS encapsulation fields for transportation of the frames over another portion of the provider network. The MiM encapsulations use provider network MAC addresses which enables VPLS MAC learning to occur using provider network MAC address space. MiM tunnels are mapped to VPLS service instances which are assigned pseudowire tags for transportation over the VPLS portion of provider network. The MiM header is retained when the MiM encapsulated frames are transported over the VPLS portion of the provider network. As VPLS frames exit the core network, the VPLS encapsulation fields are removed to extract the original MiM encapsulated frames for further transportation over the MiM portion of the provider network.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/785,527, filed May 24, 2010, now U.S. Pat. No. 8,085,811 which is acontinuation of U.S. patent application Ser. No. 11/540,023, filed Sep.30, 2006, now U.S. Pat. No. 7,746,892 and also claims the benefit of andpriority from U.S. Provisional Patent Application No. 60/732,895, filedNov. 2, 2005, entitled “Virtual MiM LAN service”, the content of each ofwhich is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to communication networks and, moreparticularly, to a method and apparatus for transporting Ethernetservices, where the Ethernet service itself might be used to carry othernative services.

2. Description of the Related Art

Data communication networks may include various computers, servers,nodes, routers, switches, bridges, hubs, proxies, and other networkdevices coupled together and configured to pass data to one another.These devices will be referred to herein as “network elements.” Data iscommunicated through the data communication network by passing protocoldata units, such as frames, packets, cells, or segments, between thenetwork elements by utilizing one or more communication links Aparticular protocol data unit may be handled by multiple networkelements and cross multiple communication links as it travels betweenits source and its destination over the network.

The various network elements on the communication network communicatewith each other using predefined sets of rules, referred to herein asprotocols. Different protocols are used to govern different aspects ofthe communication, such as how signals should be formed for transmissionbetween network elements, various aspects of what the protocol dataunits should look like, how packets should be handled or routed throughthe network by the network elements, and how information associated withrouting information should be exchanged between the network elements.

Large communication networks generally include subscriber networks,provider-based access networks, and core networks. Subscriber networksare commonly referred to as Local Area Networks (LANs), such as may beimplemented by a corporation or university, or even in a residence.Access networks are used to aggregate traffic from a large number ofsubscribers, and generally encompass an area such as a metropolitan areaor regional geographic area. Core networks are generally used totransport data between access networks. Access and core networks mayexist in many different geographic areas and may be connected in myriaddifferent ways.

Traditionally, Local Area Networks (LANs) have implemented a networkprotocol such as Ethernet to enable network elements on the LANcommunicate with each other. Ethernet is a well known networkingprotocol that has been defined by the Institute of Electrical andElectronics Engineers (IEEE) 802 Groups. Conventionally, Ethernet hasbeen used to implement networks in enterprises such as businesses andcampuses, and other technologies have been used to transport networktraffic in the access and core networks. Specifically, network providerssuch as carriers that sell bandwidth to subscribers on the access andcore networks were reluctant to deploy networks based on Ethernettechnology, since Ethernet was designed to provide best efforts serviceand did not support various control and management functions that weredeemed necessary by network providers. As the Ethernet specificationshave evolved, however, and as advancements have been made to Ethernettechnology, some of these issues are being resolved. Consequently, manyservice providers are starting to use Ethernet to implement portions oftheir networks.

It is not uncommon for networks to be connected to enable packets toflow from a subscriber's LAN over access and core networks (which may beprovided by a service provider or another entity), and then back onto adifferent portion of the subscriber's LAN. To enable this to happen, theparticular manner in which the packet is handled may make a largedifference as to the amount of coordination required between the variousnetworks.

Networks may be viewed as having three layers—a data layer, a controllayer, and a management layer. The data layer is related to how data isactually transmitted on the network. The control layer is related to howthe network elements on the network interoperate. The management layeris related to how operation of the network may be monitored so thatfaults may be detected and corrected in a timely manner.

Depending on who owns which portions of the network, it may be desirablefor one or more of the network areas to have shared control ormanagement planes. For example, a network provider may own accessnetworks in multiple cities and may want them to be commonly managed andto share control information. Depending on the particular way in whichthe networks are connected, it may be necessary for the networks to worktogether so that control and data may be passed between the networks.This type of interworking may require significant coordination and maybe difficult to implement in situations where one service provider doesnot own all sections of the network.

SUMMARY

Frames of customer traffic may be encapsulated using Mac-in-Mac (MiM)encapsulation and the MiM encapsulated traffic may be furtherencapsulated using Virtual Private LAN Service (VPLS) encapsulation. TheMiM encapsulation uses provider network MAC addressing and includeservice tags to identify service instances associated with theencapsulated frame. The MiM encapsulated frames are mapped to VPLSservice instances and encapsulated using VPLS encapsulation fortransportation over the core network. The MiM encapsulation is addedwhen the customer service frames are transported over the MiM network.As frames arrive at the edge of MiM network, the service provider MACaddresses are used as part of the MiM encapsulation. In addition, MiMencapsulation also includes a tag which identifies the MiM tunnel overwhich various MiM service instances can be carried. This tag is used toidentify the correct VPLS service instance and the service provider MACaddresses are used to identify the correct path within the VPLS network.Or in other words, the service provider MAC address space is used forVPLS MAC learning. A pseudowire tag is assigned for each MiM tunnel sothat multiple MiM tunnels may use the same VPLS path in the corenetwork. The encapsulation methods described herein may be used totransport Ethernet services, which may be point-to-point,point-to-multipoint, and multipoint, and which may be used to carryframes belonging to other services such as IP frames.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present invention are pointed out with particularity inthe appended claims. The present invention is illustrated by way ofexample in the following drawings in which like references indicatesimilar elements. The following drawings disclose various embodiments ofthe present invention for purposes of illustration only and are notintended to limit the scope of the invention. For purposes of clarity,not every component may be labeled in every figure. In the figures:

FIG. 1 is a functional block diagram of an example communication networkconfigured to transport data using MiM and VPLS encapsulations accordingto an embodiment of the invention;

FIG. 2 is a functional block diagram of a portion of the examplecommunication network of FIG. 1 showing portions of the networks ingreater detail according to an embodiment of the invention;

FIG. 3 is a functional block diagram of the encapsulation used in eachpart of the communication network of FIG. 1 according to an embodimentof the invention;

FIG. 4 is a flowchart illustrating a process of using MiM and VPLSencapsulation to transport data across a network according to anembodiment of the invention;

FIG. 5 is a functional block diagram graphically illustrating anencapsulation process for a particular service instance; and

FIG. 6 is a functional block diagram of a network element that may beused to perform encapsulation/decapsulation according to an embodimentof the invention.

DETAILED DESCRIPTION

The following detailed description sets forth numerous specific detailsto provide a thorough understanding of the invention. However, thoseskilled in the art will appreciate that the invention may be practicedwithout these specific details. In other instances, well-known methods,procedures, components, protocols, algorithms, and circuits have notbeen described in detail so as not to obscure the invention.

FIG. 1 illustrates an example network 10 in which customer traffic froma customer LAN 12A may be transported across an access network 14A, acore network 16, back through a second access network 14B, and then toanother customer network 12B. As discussed in greater detail below, theEthernet services from the customer network may be encapsulated usingMac-in-Mac (MiM) encapsulation in the access networks 14A, 14B. This MiMencapsulation may be carried out using the procedures set forth in IEEE802.1ah draft standard, although other encapsulation processes may beused as well. For example, as changes are made to the draft standard,the changes may be implemented to cause the encapsulation process tocontinue to comply with the standard. The MiM encapsulated traffic maybe further encapsulated using Virtual Private LAN Service (VPLS)encapsulation in the core network. The particular way in which MiMencapsulation and VPLS encapsulation is implemented (as discussed ingreater detail below) enables the data planes, control planes, andmanagement planes of the access and core networks to be independent sothat interworking of these planes is minimized.

FIG. 2 illustrates a portion of the network of FIG. 1 in greater detail.As shown in FIG. 2, each network area (e.g. each access and corenetwork) has Provider Edge (PE) network elements 18 configured tointerconnect the area of the network with another network or customer.The network areas also have network elements that only are connected toother network elements within the network area. These network elementsare referred to herein as P network elements 20.

A provider may set up a MiM tunnel between a first edge PE 18A on accessnetwork A to a second Edge PE on access network B 18B. Since there maybe many edge PEs on the access networks, many MiM tunnels may beestablished. Once these MiM tunnels are established, customer trafficassociated with customer service instances may be mapped to the MiMservice instances. This may be accomplished by selecting an I-SID valuefor the service instance via end-to-end control plane between the accessnetworks without input from the core network. These MiM serviceinstances are then mapped to MiM tunnels. This may be accomplished byselecting a tag for the tunnel, again via end-to-end control planebetween the access networks without input from the core network, or byselecting pre-established MiM tunnels.

The MiM tunnels need to be mapped to VPLS service instances over thecore network. The core network has a number of edge PEs 22. The corenetwork may establish paths (e.g. MPLS Label Switched Paths or othertypes of paths) through the core network via P network elements 24 thatmay be used to carry traffic belonging to VPLS service instances throughthe core network. These paths through the core network may be used bymany different VPLS service instances, and traffic belonging todifferent VPLS service instance may be differentiated using tags (e.g.pseudo wire tags) as discussed in greater detail below.

In operation, customer traffic will be carried on a particular serviceinstance that is negotiated end-to-end by the access networks. Theservice instance will be assigned to a particular MiM service instancewhich is mapped to a specific MiM tunnel through the access network A.The MiM encapsulation uses source and destination MAC addresses whichare MAC addresses in the access networks A and B. Multiple servicesinstances identified by I-SID may be carried on a given MiM tunnel.

The core edge PE 22 will perform MAC address learning on its ingress PEby looking at the MAC addresses of the MiM encapsulated frame. The corenetwork will determine which VPLS service instance should be used tocarry the traffic for the MiM tunnel and assign a tag to the MiM tunnelso that multiple MiM tunnels may be multiplexed across a given VPLS pathbetween core edge PEs 22. When traffic is received at the core networkingress, the traffic will be encapsulated by applying the tag toidentify the VPLS instance and another tag to identify the VPLS path. Inthis manner the MiM traffic from the access network may be carriedtransparently across the core network.

FIG. 3 illustrates the format of the headers that may be used to performMiM and VPLS encapsulation as described herein. As shown in FIG. 3,client frames are carried without modification as the client payload 30of a Mac-in-Mac encapsulated frame. Mac-in-Mac encapsulation is beingdefined in IEEE draft 802.1ah, the content of which is herebyincorporated herein by reference. As mentioned above, otherencapsulation processes may be used as well, for example as the 802.1ahdraft standard continues to evolve.

As shown in FIG. 3, the MiM encapsulation causes a MiM encapsulationfields 32 to be applied to the client payload 30 so that the accessnetwork is able to use its own MAC address space to forward trafficacross the access network. A physical transport header 34 may also beapplied to enable the traffic to be handled by the network. The formatof the physical transport header 34 will depend on the particulartechnology that has been deployed in the access network. For example,the physical transport header 34 may be a SONET header, a GenericFraming Procedure (GFP) header, or another type of header.

The MiM encapsulation fields 32 include the source and destination MACaddresses which are the end-points within the MiM tunnel. TheDestination MAC Address (B-DA) 38 is the MAC address in access network Bwhich is the destination address of the MiM tunnel end-point. B-DA isbased on the access network MAC address space and may be, for example,the MAC address of the ingress port of the egress PE in access networkB. Since the MiM encapsulated frames are addressed in a manner that doesnot rely on the customer MAC address space, the customer's MAC addressspace is hidden from both the access network and the core network so itis not necessary to ensure that the customers use globally unique MACaddresses.

The Source MAC Address (B-SA) 40 is the source address of the MiM tunnelend-point. B-SA is based on the source MAC address in access network Awhere the MiM tunnel originates. For example, this may be the MACaddress of the egress port of the ingress PE in access network A.

A given MiM tunnel will extend between one or more pairs of SA/DA MACaddresses. Since many subscribers may need to send traffic between thoseendpoints, it would be good to enable the traffic to be multiplexed ontothe MiM tunnels. To do this, service instances are used. A given MiMtunnel may carry multiple MiM service instances. The MiM serviceinstances may be distinguished on the MiM tunnels using the I-Tag 44.The I-Tag includes the 802.1ah Ethertype value. A B-Tag (802.1adEthertype) is included to limit the broadcast domain for MiM tunnels.The MiM encapsulation fields 32 may also include a payload Ethertypefield 36 indicating the particular Ethertype of the client payload.

The portions of the MiM encapsulation fields may be used as follows.Initially, the access network provider may establish tunnels between endpoints on the access network. These are the MiM tunnels. MiM serviceinstances will be mapped to the MiM tunnels and client traffic will bemapped to the MiM service instances. Traffic belonging to different MiMservice instances may be identified by the I-Tag values so that thetraffic may be separated at within the MiM tunnels.

When a client frame is received at an ingress PE, the ingress PE may usethe client frame's VLAN ID to set the I-Tag which contains the I-SID.The ingress PE may determine which MiM tunnel should be used to carrythe frame and set the set the B-SA, B-DA and B-VID fields so that theMiM encapsulation fields include the correct MAC addresses for the MiMtunnel. The physical transport header may then be applied and the packetwill be transported across the access network.

When the frame arrives at a core network ingress PE, the access networkpayload, including the client payload 30 and the MiM encapsulationfields, may be encapsulated by applying a VPLS encapsulation fields 50to the frame. The VPLS payload in the core network 52 is the entire MIMencapsulated frame, including the MIM encapsulation fields and theclient payload. The physical header 34 will be stripped from the MiMframe before VPLS encapsulation.

The core network ingress PE maps MiM frames to particular VPLS serviceinstances. Each VPLS service instance extends between a particular pairof ingress and egress PE network elements on the core network and willextend along a path through the network between those PE networkelements. Depending on the number of PE network elements on the corenetwork there may therefore be many service instances.

The ingress PE on the core network performs mapping of MiM tunnels,identified by the MiM tunnel tag, to VPLS service instance and MAClearning for MiM tunnels to learn the VPLS path that is to be used tocarry MiM encapsulated traffic from each of the MiM tunnels that sendtraffic to the ingress PE. Since the MiM encapsulated frames containsMAC addresses that have been assigned by access network A and accessnetwork B, the MAC learning in VPLS is based on access network MACaddress space. The MAC address space associated with the access networksis more likely to be stable, compared to customer MAC address space, andthus MAC learning of provider MAC addresses may be expected to be morerobust than if customer address space was used. VPLS is defined by theIETF L2VPN working group, and is intended to be compliant with standardsproposed by that working group.

The core network will also assign a physical transport header 58 to theframe to enable the core network to transport the frame across thenetwork. The format of the physical transport header 58 in the corenetwork, like the physical transport header 34 in the access network,will depend on the technology being used to implement the core network.

At the core network egress PE, the pseudowire tag 56 is used by theegress PE to route the frame to the correct egress port/interface. TheVPLS header 50 and core network physical header 58 will be removed atthe core network egress PE so that the MiM frames that were transportedas the access network payload 52 may be transmitted to the ingress PE onaccess network B.

Since the MiM header was transported transparently across the corenetwork, the frame may be forwarded by the ingress PE on access networkB to the intended egress PE on access network B as defined by the accessnetwork B destination address B-DA 38. A new physical transport headerwill be added at the ingress PE on access network B, the format of whichwill depend on the particular technology used to implement the accessnetwork B.

When the frame arrives at the egress PE on access network B, the egressPE on access network B will use the I-SID in the I-TAG to identify theVLAN associated with the frame. This value may be used to forward theframe to the correct customer LAN without requiring the egress PE toperform an inspection of customer frame header. The MiM header 32 andphysical transport header 34B will be removed before the frame isforwarded to the customer LAN.

Since the frame that was received from the customer LAN by accessnetwork A was directly carried as the client payload, the frame that isreceived by the customer LAN will contain all of the original headerinformation, etc. that was included with the frame when it was receivedat access network A. Thus, transportation of the client frames over theaccess and core networks may be transparent to the client. Similarly,the MiM frame output from the core network is the same as the MiM framethat was input to the core network, which makes transportation of theframes over the core network transparent to the access networks.

From a control plane perspective, the core network will treat all framesreceived from the access network as ordinary data frames. Thus, controlframes that are being used to exchange control information in the accessnetwork will be transported transparently across the core network. Thisenables the control planes for the access network to be end-to-end.Stated differently, access network A and access network B may share acommon control plane. The control plane may be anything, for exampleMultiple Registration Protocol (MRP), Generalized MPLS (GMPLS),provisioned, and the invention is not limited to the particular controlplane selected to implement the access network control plane.

Since the access network control plane frames are transportedtransparently across the core network, and are not processed or used bythe core network, the core network may maintain its own control planeindependently. Thus, interworking between the access network and corenetwork at the control level is not required. Although the accessnetwork and core network may exchange control information with eachother if desired, in ordinary operation the core network may transportcontrol packets just like any other data packets and may not treat theaccess network control packets in a special manner.

Network management may be used to monitor network conditions to identifynetwork problems and optionally to isolate the location of networkproblems once they occur. One way to do this is to inject Operation,Administration and Maintenance (OAM) frames at selected points in thenetwork and then look for the OAM frames at another point or points inthe network. Monitoring OAM flows may enable parts of the network to bemonitored for faults, and for faults to detected and isolated.

Since the core network will transparently transport any frame itreceives from the access network, access network OAM flows may existbetween the access networks. Stated another way, the core network treatsthe end-to-end access network OAM frames as regular data packets andthus, the core network treatment of OAM frames is no different than thedata plane frames. The transparent transmission of OAM frames across thecore network enables a common management plane to be used for accessnetwork A and access network B, so that management flows may existend-to-end within the access network. Similarly, management entities maybe defined within each of access network A and access network B, so thatthe access networks may independently be managed. The core network mayalso implement its own management plane without requiring the corenetwork management plane to be interworked with the access networkmanagement plane(s).

Where the core network and access network are owned by the same serviceprovider, it may be desirable to interwork the management planes ofthese two networks, for example by defining management flows that spanacross boundaries between the network areas. The invention is notlimited to an embodiment in which there is no interworking between thecore and access networks. Rather, as noted above, the solution describedherein enables the two networks to be independently managed if desired,so that interworking between the core and access networks is not aprerequisite to management of any one of them. Ethernet OAM flows may beused to perform network management as described in greater detail inco-pending U.S. patent application Ser. No. 10/880,876, entitled“Ethernet OAM Domains and Ethernet OAM Frame Format”, the content ofwhich is hereby incorporated herein by reference. Ethernet OAM flows arealso defined in ITU standard Y.1731, the content of which is herebyincorporated herein by reference.

FIG. 4 illustrates a process of transporting a customer frame across acommunication network in which MiM encapsulation is used in the accessnetwork and VPLS encapsulation is used in the core network. FIG. 5illustrates graphically the encapsulation process for a particularservice instance.

When a service frame is received at the access network ingress PE (100)the ingress PE 80A will look at the provider VLAN ID (also referred toas the S-VID contained in the S-TAG) associated with the frame and usethe provider VLAN ID to identify a MiM service instance 82 for thatframe. The MiM service instance (reference 82 in FIG. 5) is a constructin the access network which extends end-to-end across the access networkso that the access network may maintain VLAN traffic isolated to enableit to provide VPN service to its customers. The MiM service instance isidentified by the I-Tag 44 and may extend, for example, between theinput port 84A on the access network ingress PE 80A and the output port88B on the access network egress PE 90B

The MiM service instance will be carried in a MiM tunnel defined betweenend points (B-SA 40 and B-DA 38) in the access network. Unlike the MiMservice instance, the MiM tunnel may extend between the output port 88Aon the access network ingress PE 80A and the input port 84B on theaccess network egress PE 90B. Since the MiM service instances extendfrom the input ports 84A of the access network input PE 80A rather thanthe output port 88A of the access network input PE 80A, many MiM serviceinstances may be carried on one MiM tunnel. As described above, theI-TAG 44 is included in the MiM header (see FIG. 3) so that the accessnetwork egress PE may identify the service instance associated with theframe without looking at the client payload.

When the frame is received (100) the customer frame will be encapsulatedfor transmission over the access network as a MiM encapsulated frame(102). The encapsulated frame will then be transported over the MiMtunnel from the access network A ingress PE 80A to the access network Aegress PE 90A (104). The access network A egress PE will then transmitthe MiM encapsulated frame to the core network ingress PE 92 (106).

The core network ingress PE 92 will use the entire MiM encapsulatedframe as a payload in a VPLS encapsulated frame. Specifically, the corenetwork ingress PE 92 will remove the physical transport header from theframe and encapsulate the MiM encapsulated frame to form a VPLSencapsulated frame. The core network ingress PE 92 will use the B-TAG 38to determine which VPLS service instance, represented by the pseudowiretag 56, should be used to carry the frame and select the appropriateVPLS tunnel tag 54 based on B-DA.

Once the frame has been encapsulated, the VPLS encapsulated frame willbe transported over the core network (110) to the core network egress PE94. The core network egress PE 94 will remove the VPLS encapsulationfields to extract the MiM encapsulated frame. The core network egress PE94 will use the pseudowire tag 56 to identify the interface for the MiMtunnel and forward the frame out over a port associated with the MiMtunnel to the access network B (114).

The access network ingress PE 80B will receive the MiM encapsulatedframe and transport the MiM encapsulated frame over the access network B(116). Since the MiM encapsulation has been transported over the corenetwork without modification, it is only necessary to attach theappropriate physical header for access network B before forwarding theMiM encapsulated frame on the access network B.

When the MiM encapsulated frame arrives at the access network B egressPE 90B, it will be unencapsulated. Specifically, the access network Begress PE 90B will remove the MiM encapsulation to recreate the customerframe (118). The I-SID contained in the I-Tag may then be used toidentify the correct VLAN and port over which the customer frame shouldbe forwarded (120) without requiring the egress PE to perform a lookupon the header of the customer frame to identify the VLAN ID of thecustomer frame.

FIG. 6 illustrates one embodiment of a network element that may beconfigured to implement an embodiment of the invention. The networkelement may be used to implement one of the PE network elements 80A,80B, 90A, 90B, 92, and/or 94 of FIG. 5. The invention is not limited toa network element configured as illustrated, however, as the inventionmay be implemented on a network element configured in many differentways. The discussion of the specific structure and methods of operationof the embodiment illustrated in FIG. 5 is intended only to provide oneexample of how the invention may be used and implemented in a particularinstance. The invention more broadly may be used in connection with anynetwork element configured to handle Ethernet frames and other types ofprotocol data units in a communications network.

As shown in FIG. 6, the network element generally includes Input/Output(I/O) cards 150 configured to connect to links in the communicationsnetwork. The I/O cards 150 may include physical interfaces, such asoptical ports, electrical ports, wireless ports, infrared ports, orports configured to communicate with other conventional physical media,as well as configurable logical elements capable of operating as MAC(layer 2) ports.

One or more forwarding engines 152 are provided in the network elementto process frames received over the I/O cards 150. The forwardingengines 152 forward frames to a switch fabric interface 154, whichpasses the packets to a switch fabric 156. The switch fabric 156 enablesa frame entering on a port on one or more I/O cards 150 to be output atone or more different ports in a conventional manner. A frame returningfrom the switch fabric 156 is received by one of the forwarding engines152 and passed to one or more I/O cards 50. The frame may be handled bythe same forwarding engine 152 on both the ingress and egress paths.Optionally, where more than one forwarding engine 152 is included in thenetwork element, a given frame may be handled by different forwardingengines on the ingress and egress paths.

The invention is not limited to any particular forwarding engine 152,switch fabric interface 154, or switch fabric 156, but rather may beimplemented in any suitable network element configured to handleEthernet frames and/or other protocol data units on a network. One ormore Application Specific Integrated Circuits (ASICs) 158, 160 andprocessors 162, 164 may be provided to implement instructions andprocesses on the forwarding engines 152. Optionally, a memory 166 may beincluded to store data and instructions for use by the forwardingengines.

The I/O cards 150, forwarding engine 152, switch fabric interface 154and switch fabric 156, form a data plane for the network element. One ormore of the components in the data plane is configured, according to anembodiment of the invention, to handle the Ethernet frames by adding orremoving the MiM encapsulation fields 32, access network physicaltransport headers 34A, 34B, VPLS encapsulation fields 40, and/or corenetwork physical transport headers 58, as discussed above. Theparticular headers to be added will depend on whether the networkelement is being used as an access network PE 18, or as a core networkPE 22.

The network element also has a control plane configured to exchangecontrol packets with other network elements so that the correctencapsulation fields may be applied to frames as they are received. Todo this, the control plane includes at least one processor 170containing control logic 172. The processor may interface a memory 174to retrieve data and instructions that will enable the control logic toexecute control software 176 configured to enable the network element toperform control functions on the network. The memory may also includemanagement software 178 configured to enable the network element toparticipate in OAM management flows on the network as discussed ingreater detail above. Actions to be taken by the data plane may beprogrammed into the data plane by the control plane so that the dataplane may operate on frames in the manner described above.

It should be understood that all functional statements made hereindescribing the functions to be performed by the methods of the inventionmay be performed by software programs implemented utilizing subroutinesand other programming techniques known to those of ordinary skill in theart. When the functions described herein are implemented in software,the software may be implemented as a set of program instructionsconfigured to operate in control logic on a network element that arestored in a computer readable memory within the network element andexecuted on a microprocessor.

Alternatively, all or some of the functions described herein beimplemented in hardware, firmware, or a combination of hardware,software, and firmware. For example, it will be apparent to a skilledartisan that all or many of the functions described herein can beembodied using discrete components, integrated circuitry such as anApplication Specific Integrated Circuit (ASIC), programmable logic usedin conjunction with a programmable logic device such as a FieldProgrammable Gate Array (FPGA) or microprocessor, or any other deviceincluding any combination thereof. Programmable logic can be fixedtemporarily or permanently in a tangible medium such as a read-onlymemory chip, a computer memory, a disk, or other storage medium.Programmable logic can also be fixed in a computer data signal embodiedin a carrier wave, allowing the programmable logic to be transmittedover an interface such as a computer bus or communication network. Allsuch embodiments are intended to fall within the scope of the presentinvention and the invention is not limited to a particularimplementation.

It should be understood that various changes and modifications of theembodiments shown in the drawings and described in the specification maybe made within the spirit and scope of the present invention.Accordingly, it is intended that all matter contained in the abovedescription and shown in the accompanying drawings be interpreted in anillustrative and not in a limiting sense. The invention is limited onlyas defined in the following claims and the equivalents thereto.

What is claimed is:
 1. A method of transporting Ethernet services overan MPLS network, the method comprising: receiving, by a network elementon the MPLS network, a provider-network-encapsulated client frame, theprovider-network-encapsulated client frame being encapsulated accordingto IEEE 802.1ah and comprising a destination MAC address field, a sourceMAC address field, a B-Tag field, and an I-Tag field; determining aVirtual Private LAN Service (VPLS) service instance on the MPLS networkbased on the B-Tag field of the provider-network-encapsulated clientframe; and further encapsulating the provider-network-encapsulatedclient frame with VPLS-encapsulation fields corresponding to the VPLSservice instance for transportation on the MPLS network to provide aVPLS-encapsulated frame.
 2. The method of claim 1, wherein theVPLS-encapsulation fields comprise a tunnel tag having a value dependenton a value in the destination MAC address field.
 3. The method of claim1, wherein the VPLS-encapsulation fields comprise a pseudowire taghaving a value dependent on a value in the B-Tag field.
 4. The method ofclaim 1, wherein the client payload field comprises an Ethernet frame,the Ethernet frame comprising an Ethernet header and client data.
 5. Themethod of claim 1, further comprising forwarding the VPLS-encapsulatedframe on the MPLS network.
 6. The method of claim 1, wherein theprovider-network-encapsulated client frame is received from a providernetwork, the provider network being compliant with IEEE 802.1ah.
 7. Themethod of claim 1, further comprising performing VPLS MAC learning basedon contents of source MAC address fields of receivedprovider-network-encapsulated client frames.
 8. The method of claim 1,further comprising: receiving, from the MPLS network by the networkelement, a VPLS-encapsulated frame; and removing VPLS-encapsulationfields of the VPLS-encapsulated frame to provide aprovider-network-encapsulated frame.
 9. The method of claim 8, furthercomprising forwarding the provider-network-encapsulated frame onto aprovider network.
 10. The method of claim 9, wherein the providernetwork is compliant with IEEE 802.1ah.
 11. A network element fortransporting Ethernet services over an MPLS network, the network elementcomprising: at least one port configured to receive aprovider-network-encapsulated client frame, theprovider-network-encapsulated client frame being encapsulated accordingto IEEE 802.1 ah and comprising a destination MAC address field, asource MAC address field, a B-Tag field, and an I-Tag field; and atleast one network processor configured: to determine a Virtual PrivateLAN Service (VPLS) service instance on the MPLS network based on theB-Tag field of the provider-network-encapsulated client frame; and tofurther encapsulate the provider-network-encapsulated client frame withVPLS-encapsulation fields corresponding to the VPLS service instance fortransportation on the MPLS network to provide a VPLS-encapsulated frame.12. The network element of claim 11, wherein the at least one networkprocessor is configured to encapsulate the provider-network-encapsulatedclient frame with VPLS-encapsulation fields comprising a tunnel taghaving a value dependent on a value in the destination MAC addressfield.
 13. The network element of claim 11, wherein the at least onenetwork processor is configured to encapsulate theprovider-network-encapsulated client frame with VPLS-encapsulationfields comprising a pseudowire tag having a value dependent on a valuein the B-Tag field.
 14. The network element of claim 11, wherein theclient payload field comprises an Ethernet frame, the Ethernet framecomprising an Ethernet header and client data.
 15. The network elementof claim 11, wherein the at least one network processor is configured toforward the VPLS-encapsulated frame on the MPLS network.
 16. The networkelement of claim 11, wherein the at least one port is configured toreceive the provider-network-encapsulated client frame from a providernetwork, the provider network being compliant with IEEE 802.1ah.
 17. Thenetwork element of claim 11, wherein the at least one network processoris configured to perform VPLS MAC learning based on contents of sourceMAC address fields of received provider-network-encapsulated clientframes.
 18. The network element of claim 11, further comprising: atleast one port configured to receive from the MPLS network aVPLS-encapsulated frame; and at least one network processor configuredto remove VPLS-encapsulation fields of the VPLS-encapsulated frame toprovide a provider-network-encapsulated frame.
 19. The network elementof claim 18, wherein the at least one network processor is configured toforward the provider-network-encapsulated frame onto a provider network.20. The network element of claim 19, wherein the at least one networkprocessor is configured to forward the provider-network-encapsulatedframe onto a provider network which is compliant with IEEE 802.1ah.